The present invention relates to the field of industrial organic synthesis, particularly to the production of phenol and acetone by the cumene method.
A well-known method for producing phenol and acetone by the oxidation of cumene with atmospheric oxygen, followed by the acid-catalyzed decomposition of cumene hydroperoxide, makes it possible to obtain both target products (phenol and acetone) at a high yield (Khruzhalov B. D., Golovanenko B. N., Co-production of phenol and acetone, Moscow, GosKhimIzdat, 1964). However, the yield of heavy byproducts, so-called “phenol resins,” of this process remains considerable.
There are known methods of producing phenol and acetone in which, in order to reduce the yield of phenol resins (also referred to as “heavies”), cumene oxidation products containing cumene hydroperoxide (CHP), cumene, and dimethylphenylcarbinol (DMPC, also referred to as dimethylbenzyl alcohol (DMBA)) are cleaved in two stages in the presence of sulfuric acid. The first stage involves decomposition of most (97 to 99%) of the CHP and synthesis of dicumyl peroxide (DCP) from DMPC and CHP at 55 to 80° C. The second stage involves adding acetone to the resulting reaction mixture containing phenol, acetone, DMPC, and DCP at a temperature of 80 to 120° C. The acetone is added in an amount equal to 1.5 to 1.8 times its initial concentration. This process is accompanied by the cleavage of the DCP formed in the first stage, decomposition of the residual CHP, and dehydration of a portion of the residual DMPC (Russian patent Nos. 2,068,404 and 2,121,477).
The aforementioned methods make it possible to markedly reduce the amount of byproducts in comparison with the one-stage decomposition processes (resin yield: 25 kg/t of phenol). At the same time, the amount of the hydroxyacetone (HA) byproduct remains high in these improved two stage processes (for example, more than 1000 ppm).
Hydroxyacetone is a source of 2-methylbenzofuran, which is difficult to separate from phenol and which has an adverse effect on the color indexes of products made from impure commercial-grade phenol. Hydroxyacetone can be removed from phenol, for example, by an alkaline treatment, but this makes the technology of the process more complicated (Vasilieva I. I., Zakhoshansky V. M., Collection of articles titled “Petrochemical and Oil Refining Processes,” SPb, Giord, 2005, p. 344).
A method is known for decomposing technical-grade CHP in a medium composed of reaction products containing up to 13 mass % of cumene at a phenol/acetone molar ratio of greater than 1 and a sulfuric acid concentration of 0.003 to 0.015 mass % (Russian Patent No. 2,291,852). The decomposition process is carried out in two stages. In the first stage, technical-grade CHP is decomposed in at least two serially connected reactors while the reaction mass is circulated at 40 to 65° C. in the presence of the sulfuric acid catalyst having a concentration of 0.003 to 0.015 mass % in the reaction mass (depending on the temperature in the reactors and the phenol/acetone ratio). The volume in which the raw material (CHP) is introduced should not be more than 10%, and in embodiments is preferably less than 5%, of the circulation volume of the reaction mass, while the circulation factor (ratio of the flow rate of the circulating mass to the flow rate of the technical-grade CHP fed as a raw material) is from 8 to 50. If the CHP conversion is equal to 95 to 99.8% under these conditions, the CHP decomposes to give phenol and acetone, and DCP is synthesized from CHP and DMPC.
In the second stage, the synthesized DCP and the residual CHP are decomposed in the final reactor at a temperature of 90 to 140° C. while half of the added sulfuric acid is first neutralized with ammonia. The hydroxyacetone yield decreases from a level of greater than 0. 1 mass % (1000 parts per million (ppm)) to 0.04 mass % (400 ppm, as mentioned in Russian Patent No. 2,291,852). However, application of this method is premised on the use of phenol that has been purified in a phenol purification system, and the purification of phenol involves additional manufacturing steps and power consumption.
Another method of CHP decomposition is a method that is carried out in two stages according to Russian Patent No. 2,142,932. This CHP decomposition process is carried out in three serially arranged mixing reactors in the first stage, and a displacement reactor in the second stage. The CHP is decomposed in the first stage under conditions close to isothermal (that is, at a temperature of 47 to 50° C. and a concentration of 0.018 to 0.020 mass % for the sulfuric acid catalyst), while the reaction mass is additionally diluted with acetone in an amount equal to 5 to 8 mass % relative to the amount of CHP supplied. Almost all of the CHP reacts in the process, and DCP forms from part of the CHP and DMPC.
The process in the second stage is carried out while the sulfuric acid is partially neutralized with ammonia to form ammonium hydrosulfate at 120 to 140° C., and while some water is added. The concentration of acid is 0.009 to 0.010 mass %. The CHP and DCP are decomposed in a reaction medium containing phenol and acetone, both of which have formed from the CHP. Additional acetone may optionally be added to the reactor if desired.
A disadvantage of the prior-art method is the presence of hydroxyacetone in the resulting phenol. The presence of hydroxyacetone has an adverse effect on the phenol quality. There is a need for a method to further reduce the amount of hydroxyacetone in the resulting phenol produced.